ENH: add bypass mode to scons build.
ENH: add bypass mode to scons build.

On windows, most C99 functions are not available, so checking for them is
wasteful. We still don't want to add platform-specific checks, but we add a
mode so that we skip the checks if requested.

git-svn-id: 77a43f9646713b91fea7788fad5dfbf67e151ece@7408 94b884b6-d6fd-0310-90d3-974f1d3f35e1

jasonmccampbell/numpy-refactor-sprint,teoliphant/numpy-refactor,teoliphant/numpy-refactor,chadnetzer/numpy-gaurdro,jasonmccampbell/numpy-refactor-sprint,teoliphant/numpy-refactor,jasonmccampbell/numpy-refactor-sprint,jasonmccampbell/numpy-refactor-sprint,Ademan/NumPy-GSoC,Ademan/NumPy-GSoC,teoliphant/numpy-refactor,chadnetzer/numpy-gaurdro,chadnetzer/numpy-gaurdro,teoliphant/numpy-refactor,Ademan/NumPy-GSoC,Ademan/NumPy-GSoC,chadnetzer/numpy-gaurdro